Research On Distributed Consistency Control And Small Signal Stability Of DC Microgrid

The Micro Grid technology represents the development tendency of distributed energy technology and acts as an integral part of future distribution electricity system.And compared with AC micro grid,the DC micro grid embraces a higher converting efficiency and can facilitate the access of distributed electricity generation unit and consumer electronics,which promise itself a broad developing prospect.Although a wealth of studies have been conducted in the field of distribution consistency of DC micro grid in recent years,most of them are done under the condition of pure DC single busbar system,which causes the limitation.With the application DC micro grid in more areas,higher demands have appeared for the compatibility,reliability and intelligent control of this system,which further leads to a lot of new problems to the distribution consistency control of DC micro grid.For instance,how to analyze the small signal stability of alternating and DC micro source parallel serial system? How to analyze the effect of consistent control on the small signal stability of system? How to control the distribution consistency of the DC micro grid with a multibus structure? How to schedule a better system with “plug and play” protocol? On the basis of the above-mentioned problems,this dissertation is going to put the emphasis on the following aspects:1)With the AC micro source linearization model and DC micro source impedance model,the AC micro source impedance model is established,which takes the wind power generation station as a study case.It analyzes and calculates the small signal model of voltage source converter of the direct-driven permanent magnet wind turbine under the synchronous rotating reference frame and the transfer functions among various state variables,and obtains the wind power generation unit d under voltage and current double closed-loop control,q axis small signal control model and the characteristic expression of output impedance.In addition,it also deduces the DC micro source with typical controlling unit and the characteristic expression of load impedance,and further analyzes the effect of different system parameter on the impedance characteristic of each unit.The results manifests that,when the changes of key parameters in the system will accordingly affect different micro source and load impedance characteristics,and further influence the small signal stability of each frequency band in the whole system.2)The application of consistency protocol in DC micro grid with AC / DC microsource parallel serial as well as its effect on the small signal stability of the system are analyzed.For the fact that the effect of consistency protocol on micro source controller equals to the self-adaption changes of droop control coefficient,and the impedance characteristics of the system will become complicated in the DC micro grid with AC / DC micro source parallel serial,the author sets up a DC micro grid impedance model with AC / DC micro source parallel serial on the basis of consistency control.Throughout the process of consistency control,this dissertation studies the effect of changes of key consistency parameters on impedance characteristics in each unit of system,and concludes the rule of small signal stability in system by virtue of impedance analysis method.The results of analysis indicate that when the alternating / direct micro source convertors are connected in the system,the oscillating convergence procedure triggered by different boundary weighting parameters will enlarge the equivalent output impedance range of converters,affect the micro source after networking and the loaded impedance ratio characteristics and negatively influence the small signal stability of the system.Therefore,special attention shall be attached when designing the consistency protocol parameters.3)The improvement method for traditional distributed control platform is studied.The distribution control platform serves as the carrier of consistency protocol,and its execution efficiency has a direct effect on the performance of control algorithm.And the traditional distributed control platform does not equip with multithreading function,nor networking physical interface,which result in its limitation.This dissertation applies Simulink,JADE,MACSimJX to construct hybrid simulation experiment platform and realizes the distributed control over DC micro grid.Based on the illustration for and realization of each unit control strategies,the author puts forward a status information receiving method on the basis of message template,ameliorates the performance of consistency control,establishes a simulation experiment environment with five DC micro grid unit nodes in three virtual machine terminals of local area network and verifies the efficiency of distributed consistency control and cooperative control of DC micro grid.4)The application of grouping consistency protocol in the DC micro grid with double bus structure is studied.Considering the features of asynchronous communication between agents and the theoretical advantages of grouping consistency protocol over the single target consistency protocol,the author employs disperse grouping consistency protocol and realizes distributed secondary voltage and current control over the high and low-voltage bus subnet of DC micro grid with double bus structure.At the same time,the corresponding distributed control simulation experiment platforms are constructed,and the efficiencies of control strategies are compared and verified.The results show that communication in the high and low-voltage bus boundary nodes is able to improve the convergence performance of disperse grouping consistency performance,make each power node obtain the network average voltage difference and current parameters with a faster speed and thus optimize the overall performance of control strategies.